A sheet or film with a foam or cell structure is often used in packaging applications. However, use of a foamed structure in paper or paperboard is not well known. This invention provides an aqueous coating system that uses chemical blowing agents to create a foam structure in a final thermally insulative dry film. The foam is applied as a thermal insulating layer to one or both sides of paper cupstock.
In the plastics industry, most foam structures, those used to form coffee cups and the like, are produced via melt processing techniques such as extrusion or compression molding in which either a physical blowing agent, such as nitrogen gas, or a chemical blowing agent, such as azodicarbonamide is used.
Most single layer paper cupstock does not possess the thermal insulative properties of non-aqueous (conventional melt processable) foam structures.
Two paper cups have been combined to produce structures which approach these properties at very high cost.
It is an object of the present invention to produce a thermally insulated cupstock and cups that perform equally to or better than two paper cups used together.
It is an object of the present invention to produce a thermal insulated cupstock and cups that are cheaper than the cost of combining two paper cups.
It is also an object of the present invention to produce a coating which has good moisture resistance (moisture barrier) and excellent grease resistance (grease barrier).